Heat exchanger

ABSTRACT

A heat exchanger has a core and header tanks. The core includes passage units stacked in a unit sacking direction and fins. Each passage unit includes a first passage member and a second passage member connected to each other such that a second fluid passage is provided therein. The passage units are stacked such that first fluid passages are provided between bent portions of the first and second passage members of the adjacent passage units. The fins are disposed inside of the passage units and held by the bent portions of the first and second passage members. The core has core end walls constructed of at least one of first side walls of the first passage members and second side walls of the second passage members. The header tanks are disposed at ends of the core and provide tank inner spaces with the core end walls.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-231125 filed on Sep. 6, 2007, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger. More particularly, the present invention relates to a heat exchanger suitably used under a high temperature, high pressure condition.

BACKGROUND OF THE INVENTION

In general, an exhaust heat recovery apparatus, a gas cooler for cooling an exhaust gas in exhaust gas recirculation apparatus, and the like are known as examples of a heat exchanger used under a high temperature, high pressure condition. The exhaust heat recovery apparatus recovers heat of an exhaust gas generated from an engine of a vehicle using a principle of heat pipe and use the heat for warming the engine or other purposes.

For example, an exhaust heat recovery apparatus described in Japanese Unexamined Patent Application Publication No. 62-268722 has an evaporation unit and a condensation unit, which form a heat pipe. The evaporation unit is disposed in an exhaust pipe of an engine to receive heat of an exhaust gas. The condensation unit is disposed in a coolant passage for transferring the heat of the exhaust gas to a coolant through an operation fluid, thereby to heat the coolant.

An evaporation unit of such an exhaust heat recovery apparatus is, for example, constructed of a heat exchanger including a core and header tanks. The core includes tubes through which an operation fluid flows and fins joined to outer surfaces of the tubes for facilitating heat exchange between the operation fluid and an exhaust gas. The header tanks are disposed at opposite ends of the core for introducing and discharging the operation fluid into and from the tubes. For example, each header tank is constructed of a tank body and a header plate. The header plate is joined to the tank body and forms a tank inner space with the tank body. The tubes are joined to the header plate to be in communication with the tank inner space.

In such a heat exchanger, the header plate serves as a separator for separating a header tank section from a core section. The header plate does not contribute the heat exchange between the exhaust gas and the operation fluid. Further, the tubes need to be inserted to the header plate during assembling.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a heat exchanger, which has a structure capable of separating a header tank section from a core section without using a header plate.

According to an aspect of the present invention, a heat exchanger includes a core and header tanks disposed at ends of the core. The core includes passage units stacked in a unit stacking direction and fins disposed inside of the passage units. Each passage unit includes a first passage member and a second passage member. The first passage member and the second passage member are coupled to each other such that a second fluid passage through which the second fluid flows is provided therein. The first passage member has a first main wall and first side walls. The first side walls extend from a first end and a second end of the first main wall and are substantially perpendicular to the first main wall. The second passage member has a second main wall and second side walls. The second side walls extend from a first end and a second end of the second main wall and are substantially perpendicular to the second main wall. The second main wall is opposed to the first main wall in the unit stacking direction. The second side walls are connected to the first side walls. The first main wall has a first contacting portion and a first bent portion. The first bent portion projects inside of the passage unit from the first contacting portion and provides a first outer space on an outer side of the passage unit. The first bent portion extends throughout from the first end to the second end of the first main wall. The second main wall has a second contacting portion and a second bent portion. The second bent portion projects inside of the passage unit from the second contacting portion and provides a second outer space on an outer side of the passage unit. The second bent portion extends throughout from the first end to the second end of the second main wall. The passage units are stacked such that the first contacting portions and the second contacting portions contact each other between the adjacent passage units, first fluid passages through which the first fluid flows are provided by the first outer spaces and the second outer spaces between the adjacent passage units, and core end walls are provided by at least one of the first side walls and the second side walls. The fins being disposed inside of the second fluid passages and held between the first and second bent portions. The header tanks provide tank inner spaces therein with the core end walls. The tank inner spaces are in communication with the first fluid passages.

Accordingly, the header tank section is separated from the core section by the core end wall. In the above structure, since the header plate for separating the header tank section from the core section is not required, the number of component parts is reduced. Also, it is not necessary to insert the passage units to the header plate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic cross-sectional view of an evaporation unit of an exhaust heat recovery apparatus according to a first embodiment of the present invention;

FIG. 2 is a perspective exploded view of the evaporation unit according to the first embodiment;

FIG. 3 is a schematic side view of a part of a core of the evaporation unit when viewed along a flow direction of an exhaust gas according to the first embodiment; and

FIG. 4 is a schematic side view of a part of a core of an evaporation unit of an exhaust heat recovery apparatus, when viewed along a flow direction of an exhaust gas, according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A first embodiment of the present invention will now be described with reference to FIGS. 1 to 3. In the present embodiment, a heat exchanger is exemplary employed as an evaporation unit of an exhaust heat recovery apparatus, which recovers heat of an exhaust gas generated from an engine of a vehicle and uses the heat for a purpose such as for an air conditioning operation.

The exhaust heat recovery apparatus generally includes the evaporation unit 1 shown in FIG. 1 and a condensation unit (not shown). The evaporation unit 1 and the condensation unit are coupled to each other such that a looped heat pipe is formed. The evaporation unit 1 and the condensation unit are, for example, arranged adjacent to each other in a horizontal direction.

The heat pipe is provided with an introducing portion for introducing an operation fluid therein. To introduce the operation fluid in the heat pipe, pressure inside of the heat pipe is reduced through the introducing portion. After the operation fluid is introduced in the heat pipe from the introducing portion, the introducing portion is sealed. For example, the operation fluid is water. The operation fluid can be another substance, such as alcohol, fluorocarbon, chlorofluorocarbon, or the like, in place of the water.

The evaporation unit 1 is disposed in an exhaust gas passage through which an exhaust gas generated from an engine flows. For example, the evaporation unit 1 is disposed in an exhaust pipe of an engine (not shown) or to be in communication with the exhaust pipe. The evaporation unit 1 performs heat exchange between the operation fluid as a first fluid and the exhaust gas as a second fluid, thereby to evaporate the operation fluid.

The condensation unit is disposed outside of the exhaust pipe. For example, the condensation unit is disposed in a coolant passage (not shown) through which an engine coolant flows. The condensation unit performs heat exchange between the operation fluid, which has been evaporated in the evaporation unit 1, and the engine coolant, thereby to condense the operation fluid.

Next, a structure of the evaporation unit 1 will be described. In the drawings, an arrow D1 denotes a direction parallel to a flow direction of the operation fluid in a core 13 of the evaporation unit 1, which is hereinafter referred to as the operation fluid passage longitudinal direction D1. An arrow D2 denotes a unit stacking direction in which passage units 2 of the core 13 are stacked. An arrow D3 denotes a flow direction of the exhaust gas passing through the evaporation unit 1. For example, the operation fluid passage longitudinal direction D1 corresponds to an up and down direction, and the unit stacking direction D2 corresponds to a horizontal direction. The exhaust gas flow direction D3 is perpendicular to the operation fluid passage longitudinal direction D1.

The evaporation unit 1 generally includes the core 13 and header tanks 14. The core 13 includes a stack of passage units 2 in which corrugate fins 12 are disposed. The stack of passage units 2 form operation fluid passages (first fluid passages) 11 through which the operation fluid flows. The operation fluid passages 11 and the corrugate fins 12 are arranged alternately in the unit stacking direction D2. The operation fluid passages 11 extend in the up and down direction. The operation fluid passages 11 are parallel to each other.

The header tanks 14 are disposed at opposite ends of the operation fluid passages 11, that is, opposite ends of the core 13. The header tanks 14 extend in the unit stacking direction D2 and are in communication with all the operation fluid passages 11. The header tanks 14 are connected to the condensation unit through tubular communication parts 15.

Each of the passage units 2 forms an exhaust gas passage (second fluid passage) 2 a therein through which the exhaust gas flows. The corrugated fin 12 is disposed inside of the passage unit 2. The passage units 2 are stacked in the unit stacking direction D2 such that the operation fluid passages 11 are formed between the adjacent passage units 2.

Each of the passage units 2 is constructed of a first plate (first passage member) 21 and a second plate (second passage member) 22. The first plate 21 and the second plate 22 have a substantially U-shaped cross-section. The first plate 21 and the second plate 22 are paired to each other such that a space for the exhaust gas passage 2 a is provided between them.

The first plate 21 has a first main wall 21 a and first side walls 21 b. The first main wall 21 a is disposed to be substantially parallel to the exhaust gas flow direction D3. Also, the first main wall 21 a extends in the operation fluid passage longitudinal direction D1. The first side walls 21 b extend from opposite ends of the first main wall 21 a with respect to the operation fluid passage longitudinal direction D1. The first side walls 21 b are substantially perpendicular to the first main wall 21 a. Also, the first side walls 21 b extend substantially parallel to the exhaust gas flow direction D3.

Likewise, the second plate 22 has a second main wall 22 a and second side walls 22 b. The second main wall 22 a is disposed to be substantially parallel to the exhaust gas flow direction D3. Also, the second main wall 22 a extends in the operation fluid passage longitudinal direction D1. The second side walls 22 b extend from opposite ends of the second main wall 22 a with respect to the operation fluid passage longitudinal direction D1. The second side walls 22 b are substantially perpendicular to the second main wall 22 a. Also, the second side walls 22 b extend substantially parallel to the exhaust gas flow direction D3.

The first and second plates 21, 22 are connected to each other such that the first and second main walls 21 a, 22 a are opposed to each other and the first and second side walls 21 b, 22 b are overlapped with each other. As such, the passage unit 2 is formed, and the space for the exhaust gas passage 2 a is provided in the passage unit 2.

The first main wall 21 a includes a first bent portion 21 c at a substantially middle position and first contacting portions 21 k at opposite sides of the first bent portions 21 c with respect to the exhaust gas flow direction D3. The first bent portion 21 c projects inside of the passage unit 2 and forms a first outer space outside of the passage unit 2. The first bent portion 21 c extends continuously over the length of the first main wall 21 a with respect to the operation fluid passage longitudinal direction D1.

Likewise, the second main wall 22 a includes a second bent portion 22 c at a substantially middle position and second contacting portions 22 k at opposite sides of the second bent portion 22 c with respect to the exhaust gas flow direction D3. The second bent portion 22 c projects inside of the passage unit 2 and forms a second outer space outside of the passage unit 2. The second bent portion 22 c extends continuously over the length of the second main wall 22 a with respect to the operation fluid passage longitudinal direction D1.

As shown in FIG. 3, each of the second side walls 22 b of the second plate 22 is bent inside of the passage unit 2 such that a step portion 22 d is formed with a height substantially equal to a wall thickness of the second side wall 22 b. Thus, the second side wall 22 b includes a base portion 22 m connecting to the second main wall 22 a, the step portion 22 d, and an opposed portion 22 e extending from the base portion 22 m through the step portion 22 d in the unit stacking direction D2. The opposed portion 22 e extends substantially parallel to the first side wall 21 b of the first plate 21. The step portion 22 d and the opposed portion 22 e provides a receiving part 22 f for receiving the first side wall 21 b of the first plate 21.

The first plate 21 is connected to the second plate 22 such that the first side walls 21 b are disposed outside of the receiving parts 22 f and opposed to the opposed portions 22 e. Further, ends 210 of the first side walls 21 b contact the step portions 22 d, and inner surfaces of the first side walls 21 b contact outer surfaces of the opposed portions 22 e.

The end 210 of the first side wall 21 b is tapered such that a surface of the end 210 is inclined outwardly as a function of distance from the first main wall 21 a. Also, an outer surface of the step portion 22 d, which contacts the end 210, is inclined to correspond to the tapered end 210. Thus, the first and second side walls 21 b, 22 b form a flat outer surface without having grooves or the like, at an end of the passage unit 2 with respect to the operation fluid passage longitudinal direction D1. That is, the outer surface of the base portion 22 m of the second side wall 22 b is coplanar with the outer surface of the first side wall 21 b. The flat outer surface is perpendicular to the operation fluid passage longitudinal direction D1.

Since the outer surface of the step portion 22 d is inclined to correspond to the tapered end 210 of the first plate 21, the step portion 22 e contacts the tapered end 210 without a clearance when the first and second plates 21, 22 are connected to each other.

The first main wall 21 a and the first side walls 21 b form corner portions 21 g between them. At the corner portion 21 g, the outer surface of the first main wall 21 a and the outer surface of each first side wall 21 b form a substantially right angle between them. Likewise, the second main wall 22 a and the second side walls 22 b form corner portions 22 g between them. At the corner portion 21 g, the outer surface of the second main wall 22 a and the outer surface of each second side wall 22 b form a substantially right angle between them.

The corrugate fin 12 is disposed inside of the passage unit 2, and located between the first and second bent portions 21 c, 22 c of the first and second plates 21, 22. Further, the corrugate fin 12 is held by the first and second bent portions 21 c, 22 c in the passage unit 2.

As shown in FIGS. 1 and 2, the passage units 2 are stacked such that the first contacting portions 21 k contact the second contacting portion 22 k of adjacent passage units 2. Thus, the core 13 is formed. In the stack of the passage units 2, the operation fluid passages 11 are formed by the first and second outer spaces provided between the outer surfaces of the first and second bent portions 21 c, 22 c of the adjacent passage units 2.

For example, the first bent portion 21 c is formed with first ribs 21 h projecting outside of the passage unit 2. Likewise, the second bent portion 22 c is formed with second ribs 22 h projecting outside of the passage unit 2. Thus, in the stack of the passage units 2, the first ribs 21 h are in contact with the second ribs 22 h of the adjacent passage units 2.

As shown in FIG. 2, tank members 3 are connected to opposite ends of the core 13 with respect to the operation fluid passage longitudinal direction D1. The tank members 3 form tank inner spaces with core end walls 13 a of the core 13, the core end walls 13 a being perpendicular to the operation fluid passage longitudinal direction D1 and constructed of the first and second side walls 21 b, 22 b of the first and second plates 21, 22. The header tanks 14 are constructed of the tank members 3.

For example, the tank member 3 has a three-dimensional shape, and has an opening on one side. The tank member 3 includes a body portion 31 and a flange portion 32. The body portion 31 has an opening and provides the tank inner space therein. The body portion 31 is configured such that the tank inner space communicates with all the operation fluid passages 11 through the opening. The flange portion 32 is formed on a perimeter of the opening of the body portion 31. The body portion 31 has a through hole 31 a. The communication part 15 is connected to the through hole 31 a.

The flange portion 32 is configured to closely contact the core end walls 13 a, that is, the first side walls 21 b, 22 b of the first and second plates 21, 22. In the present embodiment, the flange portion 32 extends in the exhaust gas flow direction D3 such that ends of the flange portion 32 with respect to the exhaust gas flow direction D3 is opposed to the ends of the core 13 with respect to the exhaust gas flow direction D3.

The flange portion 32 has tank nails (tank engagement portions) 33 at opposite ends with respect to the unit stacking direction D2 for engaging the tank member 3 with the core 13. The tank nails 33 serve as self-jigs for holding or pressing the core 13 in the unit stacking direction D2 when the tank member 3 is assembled to the core 13.

Duct members 4 are connected to opposite ends of the core 13 with respect to the exhaust gas flow direction D3. The duct members 4 provides a duct passage therein through which the exhaust gas flows. Each of the duct members 4 has a substantially tubular shape having opening at ends. The duct member 4 has a duct main portion and a duct engagement portion 41 projecting from the duct main portion toward the core 13 for engaging the duct member 4 with the core 13.

The duct engagement portion 41 serves as a self-jig for holding or pressing the core 13 and the flange portion 32 of the tank members 3 in the operation fluid passage longitudinal direction D1. The duct engagement portion 41 is integrally formed with the main portion of the duct member 4. When the duct member 4 is assembled to the core 13, the duct engagement portion 41 presses the flanges 32 of the tank members 3 in the operation fluid passage longitudinal direction D1, over the unit stacking direction D2.

For example, the duct engagement portion 41 has a substantially tubular shape having a cross-section greater than a cross-section of the main portion of the duct member 4. When the duct member 4 is connected to the core 13, the duct engagement portion 41 surrounds an outer periphery of he core 13.

In the example shown in FIG. 2, ends of the passage units 2 are fully opening in the exhaust gas flow direction D3. The duct member 4 is connected to the core 13 such that the duct main portion is in communication with the exhaust gas passages 2 a through the openings in the exhaust gas flow direction D3.

Next, a method of manufacturing the evaporation unit 1 will be described.

First, the passage units 2 are formed. The first plate 21 and the second plate 22 are connected to each other while the corrugate fin 12 is arranged between the first plate 21 and the second plate 22. At this time, the first side walls 21 b of the first plate 21 are opposed to the outer surfaces of the opposed portion 22 e of the second plate 22.

A predetermined number of passage units 2 is stacked such that the first and second main walls 21 a, 22 a of the adjacent passage units 2 contact with each other at the contacting portions 21 k, 22 k. As such, the core 13 is assembled.

Then, the tank members 3 are assembled to the opposite ends of the core 13 with respect to the operation fluid passage longitudinal direction D1. The tank members 3 are fixed to the core 13 by engaging the tank nails 33 with the ends of the core 13 with respect to the unit stacking direction D2.

Next, the duct members 4 are assembled to the opposite ends of the core 13 with respect to the exhaust gas flow direction D3. The duct members 4 are fixed to the core 13 by engaging the duct engagement portions 41 with the flanges 32 of the tank members 3, which have been fixed to the core 13.

In this way, all the component parts of the evaporation unit 1 are assembled. Then, the assembled unit is held through a jig (not shown) by allowing the jig in the unit stacking direction D2 such that a predetermined load is applied to the core 13 in the unit sacking direction D2. As such, all the component parts are preliminarily fixed. All the component parts are placed in a heating furnace while being held the preliminarily fixed condition and is heated. Accordingly, all the component parts are integrally brazed.

In this case, the adjacent passage units 2 are held such that the main walls 21 a, 22 a are in contact with each other at the contacting portions 21 k, 22 k. Thus, the adjacent passage units 2 are joined with each other through the contacting portions 21 k, 22 k by brazing. The operation fluid passages 11 are formed between the adjacent units 2.

For example, all the component parts of the evaporation unit 1 are made of stainless steel, and a brazing material is nickel alloy.

As described above, the core 13 is formed by stacking the passage units 2, which are formed by coupling the first and second plates 21, 22. The header tanks 14 are provided by the tank members 3 that are fixed to the ends of the core 13. That is, the header tank section and the core section are separated from each other by the core end walls 13 a provided by the first and second side walls 21 b, 22 b of the first and second plates 21, 22. Accordingly, in the evaporation unit 1 of the present embodiment, a header plate, which is generally required in a conventional heat exchanger, is eliminated.

Since the evaporation unit 1 does not have the header plate, the number of component parts can be reduced. Also, a step of inserting the members forming the operation fluid passages 11 is not required. Therefore, manufacturing costs reduce.

In some heat exchangers, a core has side plates at the ends with respect to a direction in which passage member are stacked for reinforcing the core. The side plates are joined with the header plates, and serve as self-jigs for holding fins in the passage member stacking direction.

In the present embodiment, on the other hand, the fins 12 are disposed inside of the passage units 2, and held by the first and second bent portions 21 c, 22 c of the first and second plates 21, 22. Therefore, the evaporation unit 1 of the present embodiment does not require the side plates.

The ends 210 of the first side walls 21 b of the first plate 21 have the tapered shape, and the ends 210 contact the outer surfaces of the step portions 22 d of the second plate 22. Therefore, in the condition where the first and second plates 21, 22 are joined to each other, the first and second side walls 21 b, 22 b form flat surfaces. As such, the core 13 have the flat end walls 13 a that are perpendicular to the operation fluid passage longitudinal direction D1. The flange portions 32 of the tank members 3 can be in closely contact with the flat end walls 13 a of the core 13. Therefore, it is less likely that the operation fluid will leak from connecting portions between the tank members 3 and the core 13.

At the corner portions 21 g, 22 g of the first and second plates 21, 22, the outer surfaces of the first and second side walls 21 b, 22 b are substantially perpendicular to the outer surfaces of the first and second main walls 21 a, 22 a. Therefore, in a condition that the passage units 2 are stacked, clearances and grooves other than the operation fluid passages 11 are not formed between the adjacent passage units 2. That is, the first and second side walls 21 b, 22 b form flat core end walls 13 a, and the flat core end walls 13 a are perpendicular to the operation fluid passage longitudinal direction D1. Since the flange portions 32 of the tank members 3 can be in closely contact with the flat end walls 13 a, it is likes likely that the operation fluid will leak from the connecting portions between the tank members 3 and the core 13.

The tank members 3 have the tank nails 33 as the tank engagement portions. When the tank members 3 are assembled to the core 13, the tank nails 33 are engaged with the core 13 and apply forces to the core 13 in the unit stacking directions D2. That is, the tank nails 33 serve as jigs for holding the core 13. Therefore, specific jigs for holding the core 13 during the brazing can be reduced. Also, assembling work is eased. Accordingly, manufacturing costs reduce.

The duct members 4 have the duct engagement portions 41. When the duct members 4 are assembled to the core 13, the duct engagement portions 41 are engaged with the core 13 and apply forces to the core in the operation fluid passage longitudinal direction D1. That is, the duct engagement portions 41 serve as jigs for holding the core 13 in the operation fluid passage longitudinal direction D1. Therefore, specific jigs for holding the core 13 during the brazing can be reduced. Also, the assembling work is eased. Accordingly, the manufacturing costs further reduce.

The first and second bent portions 21 c, 22 c of the first and second plates 21, 22 have the first and second ribs 21 h, 22 h projecting outside of the passage units 2, that is, toward the adjacent passage units 2. When the passage units 2 are stacked, the ends of the ribs 21 h, 22 h contact with each other between the adjacent passage units 2. Therefore, during the brazing, the force applied to the core 13 in the unit stacking direction D2 can be effectively transmitted toward the passage units 2 arranged inside of the core 13 through the ribs 21 h, 22 h. Accordingly, the quality of brazing of the component parts improve.

Second Embodiment

A second embodiment of the present invention will now be described with reference to FIG. 4. Component parts similar to the first embodiment are designated with like reference numerals, and a description thereof will be omitted.

In the second embodiment, a structure of the first and second plates 21, 22 is slightly different from that of the first embodiment. As shown in FIG. 4, the second main wall 22 a of the second plate 22 has a length smaller than a length of the first main wall 21 a of the first plate 21 by a thickness of the pair of first side walls 21 b of the first plate 21, with respect to the operation fluid passage longitudinal direction D1. The second side walls 22 b of the second plate 22 are generally flat and do not have the step portions 22 d of the first embodiment. When the first and second plates 21, 22 are connected to each other such that the first side walls 21 a are opposed to the second side walls 22 b from the outside, the inner surfaces of the first side walls 21 b are in contact with the outer surfaces of the second side walls 22 b.

Further, the first side wall 21 b is configured such that the end 210 of the first side wall 21 b contact the corner portion 21 g of the first plate 21 of the adjacent passage unit 2. For example, the end 210 is tapered such that the surface of the end 210 is inclined outwardly, that is, to separate from the second side wall 22 b of the second plate 22 as a function of distance from the first main wall 21 a in each first plate 21.

In the core 13, the core end walls 13 a are provided by the first side walls 21 b of the first plates 21. The core end walls 13 a are flat. Therefore, since the flange portions 32 of the tank member 3 can be closely in contact with the flat core end walls 13 a with respect to the operation fluid passage longitudinal direction D1, it is less likely that the operation fluid will leak from the connecting portions between the tank members 3 and the core 13.

Other Embodiments

In the above embodiments, the heat exchanger is exemplarily employed as the evaporation unit 1 of the exhaust heat recovery apparatus, but can be employed as various heat exchangers, such as EGR gas cooler, a radiator, an evaporator and the like.

In the first embodiment, the duct engagement portion 41 has the substantially tubular shape having the cross-section greater than the cross-section of the main portion of the duct member 4. However, the duct engagement portion 41 may have any other shape. For example, the duct engagement portion 41 can be formed as nails capable of engaging with the flanges 32 of the duct members 3.

In the first embodiment, the step portion 22 d of the second plate 22 has the tapered shape to correspond to the tapered end 210 of the first plate 21. However, the shape of the step portion 22 d is not limited to the above, and the step portion 22 d may have any other shape.

In the first embodiment, the end 210 of the first plate 21 have the tapered shape. However, in a case where the step portion 22 d of the second plate 22 is right angled, it is not necessary to incline the end 210 of the first plate 21 as long as the end walls of the core 13 with respect to the operation fluid passage longitudinal direction D1 can be formed into flat shape.

In the second embodiment, the end 210 of the first plate 21 have the tapered shape. However, it is not always necessary to form the end 210 of the first plate 21 when the first side wall 21 b is right angled relative to the first main wall 21 a at the corner portion 21 g. That is, the end 210 may have any other shape as long as the flat wall are provided by the first side walls 21 b of the first plates 21 in the core 13.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader term is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. A heat exchanger for performing heat exchange between a first fluid and a second fluid, comprising: a core including passage units stacked in a unit stacking direction and fins disposed inside of the passage units, each passage unit including a first passage member and a second passage member coupled to each other such that a second fluid passage through which the second fluid flows is provided therein, the first passage member having a first main wall and first side walls extending from a first end and a second end of the first main wall and being substantially perpendicular to the first main wall, the second passage member having a second main wall and second side walls extending from a first end and a second end of the second main wall and being substantially perpendicular to the second main wall, the second main wall opposed to the first main wall in the unit stacking direction, the second side walls connected to the first side walls, the first main wall having a first contacting portion and a first bent portion, the first bent portion projecting inside of the passage unit from the first contacting portion and providing a first outer space on an outer side of the passage unit, the first bent portion extending throughout from the first end to the second end of the first main wall, the second main wall having a second contacting portion and a second bent portion, the second bent portion projecting inside of the passage unit from the second contacting portion and providing a second outer space on an outer side of the passage unit, the second bent portion extending throughout from the first end to the second end of the second main wall, the passage units stacked such that the first contacting portions and the second contacting portions contact each other between the adjacent passage units, first fluid passages through which the first fluid flows are provided by the first outer spaces and the second outer spaces between the adjacent passage units, and core end walls are provided by at least one of the first side walls and the second side walls, the fins disposed inside of the second fluid passages and held between the first and second bent portions; and header tanks disposed at ends of the core, the header tanks providing tank inner spaces therein with the core end walls, the tank inner spaces being in communication with the first fluid passages.
 2. A heat exchanger according to claim 1, wherein the first main wall and the first side walls have substantially right-angled outer corners therebetween, and the second main wall and the second side walls have substantially right-angled outer corners therebetween.
 3. A heat exchanger according to claim 1, wherein each of the second side walls includes a base portion connecting to the second main wall, a step portion and an opposed portion extending from the base portion through the step portion, the opposed portion is located more to inside of the passage unit than the base portion with respect to a direction perpendicular to the unit stacking direction and is opposed to the first side wall such that an outer surface of the base portion is coplanar with an outer surface of the first side wall, an end of the first side wall has an inclined surface that is inclined relative to the direction perpendicular to the unit stacking direction, and the inclined surface contacts an outer surface of the step portion.
 4. The heat exchanger according to claim 1, wherein the first side walls are overlapped with the second side walls such that inner surfaces of the first side walls contact outer surfaces of the second side walls and ends of the first side walls contact outer surfaces of the adjacent passage units, the core end walls are provided by the outer surfaces of the first side walls, and the end of each first side wall has an inclined surface that is inclined to separate from the outer surface of the second side wall as a function of distance from the first main wall in each first passage member.
 5. The heat exchanger according to claim 1, wherein each of the header tanks includes a body portion providing the tank inner space and tank engagement portions at opposite ends of the body portion with respect to the unit stacking direction, the tank engagement portions are engaged with the core and hold the core with respect to the unit stacking direction.
 6. The heat exchanger according to claim 5, wherein each of the heater tanks includes a flange portion on a periphery of the body portion, the flange portion contacts the core end wall, the heat exchanger further comprising: a duct member defining a duct passage through which the second fluid flows, the duct member connected to the core such that the duct passage is in communication with the second fluid passages provided inside of the passage units, wherein the duct member has a duct engagement portion overlapped with the flange to hold the core in the direction perpendicular to the unit stacking direction.
 7. The heat exchanger according to claim 5, further comprising: a duct member having a duct main portion with a substantially tubular shape and a duct engagement portion extending from an end of the duct main portion, wherein the duct engagement portion has a substantially tubular shape having a cross-section greater than a cross-section of the duct main portion, and the duct member is connected to the core such that the duct main portion is in communication with the second fluid passages and the duct engagement portion surrounds an outer periphery of the core.
 8. The heat exchanger according to claim 1, further comprising: a duct member defining a duct passage through which the second fluid flows, the duct member connected to the core such that the duct passage is in communication with the second fluid passage provided inside of the passage units, wherein the duct member has a duct engagement portion that is engaged with the core and hold the core with respect to a direction perpendicular to the unit stacking direction.
 9. The heat exchanger according to claim 8, wherein the passage units have openings in a second fluid flow direction that is perpendicular to the unit stacking direction and a flow direction of the first fluid in the first fluid passages, and the duct member is connected to the core with respect to the second fluid flow direction.
 10. The heat exchanger according to claim 1, wherein the first bent portion has a first rib projecting outside of the passage unit, the second bent portion has a second rib projecting outside of the passage unit, and the first rib contacts the second rib of the adjacent passage unit. 